What are GPG keys used for?

[diablo75]

I was looking over the instructions for installing medibuntu, and I got to the part where it tells you to paste in a certain command to add the GPG keys. I'm just curious... what is the purpose of this?

[LaRoza]

I was looking over the instructions for installing medibuntu, and I got to the part where it tells you to paste in a certain command to add the GPG keys. I'm just curious... what is the purpose of this?
Are you asking what they are used for, or what they are? If you knew what they are, the reason for using them would be obvious, I hope: http://en.wikipedia.org/wiki/GNU_Privacy_Guard